NH3 containing plasma nitridation of a layer of a three dimensional structure on a substrate

ABSTRACT

Methods and apparatus for forming nitrogen-containing layers are provided herein. In some embodiments, a method includes placing a substrate having a first layer disposed thereon on a substrate support of a process chamber; heating the substrate to a first temperature; and exposing the first layer to an RF plasma formed from a process gas comprising ammonia (NH 3 ) to transform the first layer into a nitrogen-containing layer, wherein the plasma has an ion energy of less than about 8 eV.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/790,444, filed Mar. 15, 2013, which is herein incorporatedby reference in its entirety.

FIELD

Embodiments of the present invention generally relate to semiconductorprocessing, and more particularly to methods for formingnitrogen-containing layers.

BACKGROUND

The scaling of semiconductor devices, such as dynamic random accessmemory (DRAM), logic devices, and the like, may be limited by gateleakage (J_(g)). For example, as thickness of a gate dielectric layer isscaled, current may leak between the channel and the gate of atransistor device causing device failure. The gate leakage may bereduced by incorporating nitrogen into the gate dielectric layer. Forexample, a gate dielectric layer at the 32 nm node may comprise siliconoxynitride (SiON), where the presence of nitrogen reduces gate leakagein the device.

Typically, nitrogen is incorporated into the gate dielectric layer by aplasma nitridation process that provides for gate leakage reduction atthe expense of other desired properties, for example, flat band voltage(V_(fb)), threshold voltage (V_(t)), and mobility. For example,increased nitrogen content in the gate dielectric layer may undesirablyincrease V_(t) and excessively decrease mobility. Further, oxygen maydiffuse from the gate dielectric layer under typical processingconditions, thus further reducing device performance, for example bydegrading the dielectric properties of the gate dielectric layer.

Furthermore, nitridizing a dielectric layer on a semiconductor wafer foruse in a semiconductor structure involves adding nitrogen to a planarsemiconductor structure using plasma nitridation or thermal nitridation.However, the use of 3-dimensional (“3D”) semiconductor structures, suchas a FinFET device or the like, requires a nitridized layer to wraparound the 3D semiconductor structure with the amount of nitrogenincorporated on the top surface of the 3D semiconductor structuresubstantially equal to the amount of nitrogen incorporated down thesidewalls of the 3D semiconductor structure, referred to herein asconformality. Conformality is calculated as the percentage of nitrogendrop with depth down the sidewall of the 3D semiconductor structure.

One method of forming a nitridized layer is via thermal nitridationusing ammonia (NH₃). While thermal nitridation using ammonia (NH₃)provides suitable conformality, the process fails to provide the desirednitrogen profile at the top surface of the dielectric layer. Anothermethod of forming a nitridized layer is using inductively coupled plasmanitridation with ions formed from nitrogen gas (N₂). While this approachprovides the desired nitrogen profile in the dielectric film, theresulting conformality is inadequate. While another method, remoteplasma nitridation, can provide suitable conformality, the processrequires temperatures in excess of about 600 degrees Celsius to about1000 degrees Celsius, resulting in excessive and undesirable thickeningof oxide layers in the gate stack.

Accordingly, the inventors have provided methods of forming nitrogencontaining layers having improved conformality.

SUMMARY

Methods and apparatus for forming nitrogen-containing layers areprovided herein. In some embodiments, a method includes placing asubstrate having a first layer disposed thereon on a substrate supportof a process chamber; heating the substrate to a first temperature; andexposing the first layer to an RF plasma formed from a process gascomprising ammonia (NH₃) to transform the first layer into anitrogen-containing layer, wherein the plasma has an ion energy of lessthan about 8 eV.

In some embodiments, a method of forming a nitrogen-containing layerincludes placing a substrate having a first layer disposed thereon on asubstrate support of a process chamber, wherein the first layer is a3-dimensional structure; heating the substrate to a first temperature ofabout 250 degrees Celsius to about 500 degrees Celsius; and exposing thefirst layer to an RF plasma formed from a process gas comprising ammonia(NH3) to transform the first layer into the nitrogen-containing layer,wherein the process gas comprises about 0.5% to about 99.5% ammonia(NH3) based on total gas flow and the balance is a noble gas, andwherein the plasma has an ion energy of less than about 8 eV.

The preceding brief summary is not intended to be limiting of the scopeof the present invention. Other and further embodiments of the presentinvention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a flow chart depicting a method of forming anitrogen-containing layer in accordance with some embodiments of theinvention.

FIGS. 2A-2C depict stages of fabricating a gate dielectric layer inaccordance with some embodiments of the invention.

FIG. 3 depicts a plasma nitridation reactor suitable for use inaccordance with some embodiments of the invention.

FIG. 4 depicts a substrate support suitable for use in a plasmanitridation reactor in accordance with some embodiments of theinvention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Methods and apparatus for forming nitrogen-containing layers areprovided herein. The inventive methods and apparatus may advantageouslyprovide improved nitridation of a target layer (e.g., a first layer) forexample, by facilitating increased nitrogen content, and improved oxygenretention at an interface between the target layer and another devicelayer, for example, a polysilicon gate. The inventive methods andapparatus may also advantageously improve the conformally of anitridized dielectric film atop a 3D semiconductor structure.

FIG. 1 depicts a method 110 for forming a nitrogen-containing layer inaccordance with some embodiments of the present invention. Generally,the method 110 includes providing a partially fabricated semiconductorstructure including a substrate having a first layer disposed thereon.The semiconductor structure may be a partially fabricated semiconductordevice such as Logic, DRAM, or Flash memory devices. Thenitrogen-containing layer formed by this process may be one or more of agate dielectric layer, a tunnel oxide layer, a spacer layer, or anysuitable layer of a semiconductor structure that may benefit fromnitridation, for example, to reduce junction leakage, gate leakage, orthe like.

The method 110 is described herein with respect to the partiallyfabricated semiconductor structure depicted in FIGS. 2A-D, whichrespectively depict stages of fabrication of a semiconductor structureincluding a first layer formed over a substrate. The method 110 may beperformed in any suitable plasma reactor that can provide a low energyplasma as disclosed herein, for example, such as those reactorsconfigured to provide an inductively coupled, or remote plasmas, or thelike. Embodiments of suitable plasma reactors that may be utilized withthe inventive methods are described below with respect to FIG. 3. Theplasma reactor may be utilized alone or, more typically, as a processingmodule of an integrated semiconductor substrate processing system, orcluster tool, such as a CENTURA® DPN Gate Stack integrated semiconductorwafer processing system, available from Applied Materials, Inc. of SantaClara, Calif. Other tools, including those available from othermanufacturers, may also be used.

The method 110 begins at 102, where a substrate 202 is provided having afirst layer 204 to be nitridized disposed thereon, as shown in FIG. 2A.The substrate 202 and the first layer 204 may be part of a completely orpartially fabricated semiconductor device 200. The first layer 204 maybe a 3-dimensional, or 3D, structure or a part of such a 3D structure.As used herein a 3-dimensional (or 3D) structure refers to asemiconductor structure where the transistor forms conducting channelson three sides of a vertical structure, as compared to a traditional 2Dplanar transistor which forms a conducting channel mainly under thegate. The substrate 202 may have various dimensions, such as 200 or 300mm diameter wafers, as well as rectangular or square panels. Thesubstrate 202 may comprise a material such as crystalline silicon (e.g.,Si<100> or Si<111>), silicon oxide, strained silicon, silicon germanium,doped or undoped polysilicon, doped or undoped silicon wafers, patternedor non-patterned wafers, silicon on insulator (SOI), carbon dopedsilicon oxides, silicon nitride, doped silicon, germanium, galliumarsenide, glass, sapphire, or the like.

The semiconductor device 200 may be completely or partially formed uponthe substrate 202 and includes at least the first layer 204 to benitridized. The semiconductor device 200 (when completed) may be, forexample, a field effect transistor (FET), dynamic random access memory(DRAM), a flash memory device, a 3D FINFET device, or the like. Thefirst layer 204 may be, for example, utilized as a gate dielectric layerof a transistor device, a tunnel oxide layer in a flash memory device, aspacer layer atop a gate structure, an inter-poly dielectric (IPD) layerof a flash memory device, or the like. The first layer 204 may have anythickness suitable in accordance with the particular application forwhich the first layer 204 may be utilized. For example, the first layer204 may have a thickness of about 0.5 to about 10 nm. The first layer204 may comprise an oxide layer, such as silicon oxide (SiO₂), hafniumoxide (HfO₂), hafnium silicate (HfSiO_(x)), or any suitable oxide layerused in a semiconductor device and requiring nitridation. For example,in some embodiments, the oxide layer may be a native oxide layer, orformed by any suitable oxidation process including the oxidation processdiscussed below. The first layer 204 need not be limited to an oxidelayer, and other suitable layers may benefit from the inventive methodsdisclosed herein. For example, other suitable embodiments of the firstlayer 204 may include other suitable semiconductor materials, such assilicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbide(SiC), III-V compounds, or metals, metal nitrides, or metal oxides suchas tungsten (W), titanium (Ti), tantalum (Ta), titanium nitride (TiN),tantalum nitride (TaN), titanium oxide (TiO₂), or aluminum oxide(Al₂O₃), or the like. The first layer 204 can also be a stack of layers,such as a first sub-layer of SiO₂ and a second sub-layer of HfO₂ or afirst sub-layer of SiO₂ and a second sub-layer of HfSiO_(x), or thelike.

Next, at 104, the substrate 202 may be heated prior to and duringnitridation. Heating the substrate 202 may facilitate providingincreased nitrogen content into the first layer 204 and improved deviceproperties. For example, heating the substrate 202 to a temperature ofat least about 250 degrees Celsius, or at least about 350 degreesCelsius may facilitate increased nitrogen content (e.g., an atomicpercentage content of about 5 to about 35) in the first layer 204. Insome embodiments, the substrate may be heated to a temperature of about250 to about 550 degrees Celsius, or in some embodiments, about 350 toabout 450 degrees Celsius. In some embodiments, the substrate may beheated to a temperature of about 400 degrees Celsius. The actual maximumsubstrate temperature may vary based upon hardware limitations and/orthe thermal budget of the substrate being processed.

In embodiments where the first layer 204 is an oxide layer, theincreased temperature may advantageously facilitate less evolution ofoxygen from the layer (e.g., less than about 20%) and further,accumulation of oxygen at an interface of the first layer 204 and thesubstrate 202. In some embodiments, the substrate 202 is heated to about250 to about 550 degrees Celsius. In some embodiments where the firstlayer 204 is an oxide layer, the substrate 202 may be heated to about300 to about 550 degrees Celsius, or to about 350 to about 500 degreesCelsius.

In some embodiments, the substrate 202 may be positioned in the reactorsuch that heat transfer to the substrate is maximized, for example,between the substrate 202 and a substrate support on which the substrate202 rests during the method 110. As such, the substrate 202 may besecured to the substrate support using a chucking device, such as anelectrostatic chuck (ESC), a vacuum chuck, or other suitable device.Chucking the substrate 202 may advantageously facilitate reproducibleheat transfer even at low pressures (the process pressure region), forexample, at about 4 mTorr to about 1 Torr, or at about 10 to about 80mTorr, at about 10 to about 40 mTorr, or at about 10 to about 20 mTorr.Optionally, in embodiments where an electrostatic chuck is provided tosecure the substrate 202, a second plasma may be formed above thesubstrate 202 to facilitate stabilization of the substrate temperatureas the substrate is chucked. For example, the second plasma may beformed from a non-reactive gas including at least one of argon (Ar),helium (He), krypton (Kr), xenon (Xe), or the like, to preheat thesubstrate 202 such that upon chucking the substrate 202 to the substratesupport and extinguishing the plasma, the substrate 202 does notexperience a dramatic change in temperature which could lead to processvariation and/or wafer breakage. As used herein, non-reactive gasesinclude gases that do not substantially react with the substrate (e.g.,do not substantially deposit upon or etch the substrate).

The substrate 202 may be heated by any suitable heating mechanismcapable of increasing and maintaining the substrate temperature at about250 degrees Celsius or greater or, in some embodiments, at about 350degrees Celsius or greater. Suitable heating mechanisms can includeresistive heating, radiative heating or the like. For example, and asdiscussed below in embodiments of the reactor 300, one or more resistiveheaters may be disposed in a substrate support for providing heat to thesubstrate 202. Alternatively, the substrate may be heated, for example,by one or more lamps or other energy sources disposed above and/or belowthe substrate 202.

In one heating approach, the heater elements are embedded in theelectrostatic chuck, so that the substrate is directly heated from theelectrostatic chuck. Several advantages may arise from such approach:(1) the substrate can be maintained at a constant temperature during theentire process as long as it is chucked, even though the processpressure is as low as 4 mTorr; (2) process results (nitrogen dose andpercentage of nitrogen incorporated by mass (N %)) can be reproduciblefrom substrate to substrate due to the tight control on the substratetemperature during the process; and (3) the within-substrate nitridationuniformity pattern can be altered (e.g., compensated for) by carefullydesigned heating uniformity pattern in the heater elements of theelectrostatic chuck, or by providing multi-zone heater elements havingindependent control.

In the case of using an electrostatic chuck heater, due to the nature ofchucking/heating process, the rise of the substrate temperature can bevery fast, such as up to about 30 degrees Celsius per second. Under suchhigh heating rates, there may be a chance that not every portion of thewafer will be heated at the same rate, so that at certain point, thetemperature difference within the substrate may reach a critical value(e.g., >75 degrees Celsius) which could cause the substrate (such as asemiconductor wafer) to crack. To prevent such failure, a preheat stepmay be implemented prior to substrate chucking. The preheat step mayinclude flowing a non-reactive gas, such as nitrogen (N2) or helium(He), or the like, at a rate of about 400 sccm to about 4 liter perminute, for about 20 to about 60 seconds or more (such as about 50seconds), at a pressure of about 1-10 Torr (such as about 8 Torr), whilemaintaining the electrostatic chuck heater at the desired temperature(such as about 400 degrees Celsius) with the substrate disposed on thesurface of the electrostatic chuck but not chucked thereto. The preheatstep facilitates bringing up the substrate temperature close to theelectrostatic chuck temperature prior to chucking (for example to withinabout 150 degrees Celsius of a targeted temperature of the substrate),hence reducing the potential thermal shock to the substrate uponchucking the substrate. In some embodiments, when a low contactelectrostatic chuck (e.g., an electrostatic chuck having up to about 5%contact area) is utilized to support the substrate, a backside gas maybe utilized to preheat the wafer. In some embodiments, the substrate maybe preheated prior to delivery into the process chamber, such as bycontact or non-contact (e.g., lamp) methods.

Optionally, prior to nitridation of the first layer 204, the processchamber may be pre-conditioned to reduce residual oxygen content in theprocessing volume. For example, residual oxygen content such as frommoisture, water (H₂O) or the like may result in undesired parasiticoxidation of the substrate 202 or the first layer 204. To prevent thisfrom happening, the interior of the process chamber (including the lid,sidewall, and pedestal or chuck) may be pre-conditioned with apre-conditioning plasma formed from a pre-conditioning gas. Thepre-conditioning gas may include, for example, nitrogen (N₂), ammonia(NH₃), or ammonia (NH₃) and an inert gas, such as argon (Ar), or anysuitable gas and/or combination of gases that may reduce the moisturecontent and season the chamber interior. In some embodiments, thepre-conditioning gas may consists, or consists essentially of, nitrogen(N₂), or ammonia (NH₃), or ammonia (NH₃) and an inert gas, such as argon(Ar). In some embodiments, pre-conditioning may be performed prior to,or during, chucking (e.g., securing the substrate to the chuck). In someembodiments, pre-conditioning may be performed prior to heating thesubstrate, or prior to nitridation of the first layer 204.

Next, at 106, the first layer 204 may be exposed to a radio frequency(RF) plasma formed from a process gas consisting of, consistingessentially of, or comprising ammonia (NH₃). In some embodiments, thefirst layer 204 may be exposed to the RF plasma, while maintaining theprocess chamber at a pressure of about 5 mTorr to about 500 mTorr, orabout 10 to about 80 mTorr, or about 10 mTorr to about 40 mTorr, orabout 10 mTorr to about 20 mTorr to form a nitrogen-containing layer208, as depicted in FIG. 2C. For example, in some embodiments, theprocess gas may be pure ammonia (NH₃) or a mixture of ammonia (NH₃) anda noble gas. The noble gas may be, for example, argon (Ar). In someembodiments, the process gas comprises ammonia (NH₃) and argon (Ar). Insome embodiments, the process gas may consist only of ammonia and argon.In some embodiments, the process gas may be predominantly comprised ofor may consist essentially of ammonia and argon.

In some embodiments, the process gas may be supplied at a total gas flowfrom about 100 to about 1000 sccm, or at about 400 sccm (although otherflow rates may be used depending upon the application and configurationof the process chamber). In some embodiments, the process gas maycomprise about 10-100 percent NH₃ (e.g., an NH₃ flow of between about10-1000 sccm) with the balance being essentially a noble gas forexample, argon (Ar) (e.g., a noble gas percentage of about 0 to about 90percent). In some embodiments, the process gas may comprise about 0.5-99percent NH₃ (e.g., an NH₃ flow of between about 0.5-990 sccm) with thebalance being essentially a noble gas, for example, argon (Ar) (e.g., anoble gas percentage of about 1 to about 99.5 percent). In someembodiments, the process gas may be about 1.5-50 percent NH₃ (e.g., anNH₃ flow of between about 15-500 sccm) with the balance beingessentially a noble gas, such as argon (e.g., an inert gas percentage ofabout 50 to about 98.5 percent). In some embodiments, the process gasmay comprise about 10-99 percent of the noble gas (e.g., a noble gasflow of about 100-990 sccm). In some embodiments, the process gas maycomprise about 80-99 percent of the noble gas (e.g., a noble gas flow ofabout 800-990 sccm).

The process gas may be introduced into a plasma reactor, for example,the plasma reactor 300, and used to form a plasma 206. In someembodiments, the plasma density may be about 10¹⁰ to about 10¹²ions/cm³. The plasma 206 may be formed by using an RF source power. Insome embodiments, the plasma 206 formed has an ion energy of less than 8eV. In some embodiments, the plasma 206 formed has an ion energy of lessthan 4 eV. In some embodiments, the plasma 206 formed has an ion energyof about 1 eV to about 4 eV. In some embodiments, the RF source power iscapable of producing up to about 2500 watts, or more. The RF sourcepower may be provided at any suitable RF frequency. For example, in someembodiments, the RF source power may be provided at a frequency about 2to about 60 MHz, such as 13.56 MHz.

The plasma 206 may be pulsed or continuously applied at up to about 1000watts effective power. For example, the plasma 206 may appliedcontinuously at up to about 400 watts for a duration of about 10 toabout 400 seconds, or about 100 seconds. The duration may be adjusted(e.g., shortened) to limit damage to the semiconductor device 200.Alternatively, the plasma 206 may be pulsed at a pulse frequency ofabout 4 kHz to about 15 kHz. The pulsed plasma may have a duty cycle ofabout 2% to about 30%, at up to 2500 watts peak power, where the dutycycle and/or RF source power may be adjusted to limit damage to thesemiconductor device 200. In some embodiments, the plasma 206 may bepulsed at a duty cycle of up to 20% at up to 2000 watts peak power. Insome embodiments, the plasma 206 may be pulsed at a duty cycle of about5% to about 10% at up to 2000 watts peak power.

The inventors have observed that the use of a process gas consistingessentially of either ammonia (NH₃) or ammonia (NH₃) dilute in a noblegas, in a low ion energy plasma 206, for example having an ion energyless than 8 eV, composed of NH* radicals, advantageously moreconformally nitridizes the first layer 204, for example a hafnium oxide(HfO₂) layer, such that the amount of nitrogen incorporated in the topsurface 210 of the nitrogen-containing layer 208 is substantially equalto the amount of nitrogen incorporated down the sidewalls 214 of thenitrogen-containing layer 208.

The use of an ammonia gas (NH₃), either pure or dilute in, for example,argon, in forming the low ion energy plasma 206 is advantageous overtypical nitridation processes because the NH radicals in the ammonia(NH₃)-formed plasma 206 are not affected by the field across the plasmasheath. As a result, the NH radicals arrive at the substrate 202 withoutany preferred direction and react with substrate surfaces of anyorientation, such as the top surface 210 and sidewalls 214 of the firstlayer 204, in order to conformally nitridize the first layer 204 withoutundesirable thickening of the first layer 204.

In some embodiments, the exposed surface of the substrate 202 may be atleast partially covered with a sacrificial layer (not shown), such as amasking layer to prevent exposure to the plasma 206 (e.g., to limitexposure of the plasma to desired portions of the substrate 202 and/orthe first layer 204). In some embodiments, a pressure in the plasmareactor may be up to about 80 mTorr, about 10 mTorr to about 80 mTorr,about 10 mTorr to about 40 mTorr, or about 10 to about 30 mTorr duringthe exposure of the first layer 204 to the plasma 206.

The nitrogen-containing layer 208 formed from exposure of the firstlayer 204 to the plasma 206 as discussed above may be, for example,utilized as a gate dielectric layer of a transistor device, a tunneloxide layer in a flash memory device, a spacer layer atop a gatestructure, in an inter-poly dielectric (IPD) layer of a flash memorydevice, or the like. The nitrogen-containing layer 208 may have athickness of about 0.3 to about 10 nm. The nitrogen-containing layer 208may have a nitrogen content of about 3 to about 25 atomic percent. Thenitrogen-containing layer 208 may comprise an oxynitride layer, such assilicon oxide (SiON), hafnium oxynitride (HfON), nitridated hafniumsilicate (HfSiON), or any suitable oxynitride layer used in asemiconductor device and requiring nitridation. The nitrogen-containinglayer 208 need not be limited to an oxynitride layer, and other suitablelayers may benefit from the inventive methods disclosed herein. Forexample, in other suitable embodiments, the nitrogen-containing layer208 may include or may be replaced with SiCN or other silicon (Si)containing compounds, metal containing compounds such as titanium oxideor nitride, tantalum oxide or nitride, aluminum oxide or nitride, or thelike.

Upon forming the nitrogen-containing layer 208, the method 110 generallyends and additional process steps (not shown) may be performed tocomplete fabrication of the semiconductor device 200 and/or otherdevices (not shown) on the substrate 202.

The inventive methods described herein, for example, the method 110 canbe performed in a plasma reactor. For example, FIG. 3 depicts aschematic diagram of an inventive plasma reactor 300 adapted to be usedto practice embodiments of the invention as discussed herein. Thereactor 300 may be utilized alone or, more typically, as a processingmodule of an integrated semiconductor substrate processing system, orcluster tool, such as a CENTURA® DPN Gate Stack integrated semiconductorwafer processing system, available from Applied Materials, Inc. of SantaClara, Calif.

The reactor 300 includes a process chamber 310 having a substratesupport 316 disposed within a conductive body (wall) 330, and acontroller 340. In some embodiments, the substrate support (cathode) 316is coupled, through a first matching network 324, to a biasing powersource 322. The biasing source 322 generally is a source of up to 500 Wat a frequency of approximately 13.56 MHz that is capable of producingeither continuous or pulsed power. In other embodiments, the source 322may be a DC or pulsed DC source. In some embodiments, no bias power isprovided.

In some embodiments, the process chamber 310 may include a liner (notshown) to line the inner surfaces of the process chamber 310. In someembodiments, the liner may be cooled, for example with coolant channelsprovided within the liner to flow a coolant therethrough. In someembodiments, the process chamber 310 (and other components exposed toplasma during processing) may be coated with a material that isresistant to the plasma. For example, in some embodiments, the processchamber 310 may be coated with a material that is resistant to attackfrom the plasma. In some embodiments, the coating may comprise a quartz,or a ceramic material, such as a yttrium oxide (Y₂O₃)-based ceramiccompositions, aluminum oxide, or the like. In accordance withembodiments of the present invention, attack of chamber components fromhydrogen radicals may advantageously be reduced during processing asdescribed herein, while advantageously maintaining nitridation rates.

The chamber 310 may be supplied with a substantially flat dielectricceiling 320. Other modifications of the chamber 310 may have other typesof ceilings such as, for example, a dome-shaped ceiling or other shapes.At least one inductive coil antenna 312 is disposed above the ceiling320 (dual co-axial antennas 312, including an outer coil 312 _(A) and aninner coil 312 _(B), are shown in FIG. 3). Each antenna 312 is coupled,through a second matching network 319, to a RF power source 318. The RFsource 318 typically is capable of producing up to about 5000 W at atunable frequency in a range from 2 MHz to 13.56 MHz, and which mayproduce either a continuous or pulsed plasma. Typically, the wall 330may be coupled to an electrical ground 334.

In some embodiments, a power divider 304 may be disposed in the linecoupling the outer coil 312 _(A) and the inner coil 312 _(B) to the RFpower source 318. The power divider 304 may be utilized to control theamount of RF power provided to each antenna coil (thereby facilitatingcontrol of plasma characteristics in zones corresponding to the innerand outer coils). The dual coil antenna configuration may advantageouslyprovide improved control of nitrogen dosage within each zone, such as tothe first layer 204, as discussed above in the method 110.

Optionally, either and/or both of the antennas 312 may be tilted and/orraised lowered with respect to the ceiling 320. The change in positionand/or angle of the antenna 312 may be utilized, for example, to changethe characteristics, such as uniformity, of a plasma formed in theprocess chamber.

Further, and optionally, a plasma shield/filter may be included abovethe substrate support to provide improved control of, for example,nitridation of the first layer 204 as discussed above in the method 110.The plasma shield/filter may comprise a material, such as quartz, andmay be grounded to the chamber 310 to remove ion species from the plasmaformed in the process chamber. For example, an ion-radical shield 327may be disposed in the chamber 310 above the substrate support 316. Theion-radical shield 327 is electrically isolated from the chamber walls330 and the substrate support 316 and generally comprises asubstantially flat plate 331 having a plurality of apertures 329. In theembodiment depicted in FIG. 3, the ion-radical shield 327 is supportedin the chamber 310 above the pedestal by a plurality of legs 325. Theapertures 329 define a desired open area in the surface of theion-radical shield 327 that controls the quantity of ions that pass froma plasma formed in an upper process volume 378 of the process chamber310 to a lower process volume 380 located between the ion-radical shield327 and the substrate 314. The greater the open area, the more ions canpass through the ion-radical shield 327. As such, the size anddistribution of the apertures 329, along with the thickness of the plate331 controls the ion density in volume 380. Consequently, the shield 327is an ion filter. One example of a suitable shield that may be adaptedto benefit from the invention is described in U.S. patent applicationSer. No. 10/882,084, filed Jun. 30, 2004 by Kumar, et al., and entitled“METHOD AND APPARATUS FOR PHOTOMASK PLASMA ETCHING”. By changing the iondensity near the wafer surface, one can control the ion/radical ratio,hence, possibly controlling the nitridation profile.

In some embodiments, the substrate support 316 may include a chuckingdevice 317 for securing the substrate 314 to the support pedestal duringprocessing. For example, the chucking device 317 may include anelectrostatic chuck or a vacuum chuck. The chucking device 317 mayfacilitate improved heat transfer between the substrate 314 and one ormore resistive heaters 321 disposed in the substrate support 316. Asillustrated, the one or more resistive heaters 321 may be disposed inthe substrate support 316 generally below the position of substrate 314and configured in multiple zones to facilitate controlled heating of thesubstrate 314. In some embodiments, the substrate support 316 includesan electrostatic chuck and also includes one or more resistive heatersdisposed within or beneath the electrostatic chuck. In some embodiments,the substrate support 316 may not include an electrostatic chuck, butmay have one or more resistive heaters disposed proximate a supportsurface of the substrate support. In such embodiments, the substratesupport having the resistive heaters may have a surface coating of, forexample, aluminum nitride (e.g., the substrate support may be fabricatedfrom, or may have an outer coating of, aluminum nitride or the like).

In some embodiments, the substrate support 316 may not have anelectrostatic chuck and may include a resistive heater, such as shown inFIG. 4. The substrate support 316 depicted in FIG. 4 includes aresistive heater 321 configured to regulate the temperature of thesubstrate 314. The heater 321 may be include one or more zones (outerzone 402 and inner zone 404 depicted in FIG. 4). The heater 321 iscoupled to a power source 412 and is capable of maintaining thesubstrate 314 at a temperature of up to about 500 degrees Celsius. Insome embodiments a grounding mesh 406 may be disposed between the one ormore heaters 321 and an upper surface 416 of the substrate support 316to prevent the substrate 314 form sticking to the surface 416 of thesubstrate support 316. The inert coating discussed above may be alsoapplied to the surface 416 of the substrate support 316.

In the case of using an electrostatic chuck with a heater, it has beendemonstrated that the nitrogen dose and N % (e.g., the percentage ofnitrogen by mass incorporated into the first layer 204 to form thenitrogen-containing layer 208) is directly proportional to the wafertemperature during the plasma process. So to control and/or tune thenitrogen dose and N % uniformity on the wafer, two approaches can beutilized: (1) fixed zone heating with a pre-designed pattern of powerdensity for the heater elements so that the temperature uniformitypattern of the wafer compensates for the plasma uniformity pattern; or(2) tunable multiple zone heating with tunable power supplies fordifferent heater zones (typically center and edge dual zones, but morezones may be utilized) so that the wafer temperature uniformity can betuned to compensate for the plasma uniformity pattern. In eitherapproach, temperature may be utilized as a knob to achieve improvedwithin-wafer nitridation uniformity and/or providing a desired nitrogendose pattern in the substrate. In some embodiments, the nitrogen dosepattern may be substantially uniform (e.g., within about 1 percent).

A motion assembly 410 may be provided to control the elevation of thesubstrate support 316, and therefore, of the substrate 314 duringprocessing. The motion assembly 410 is sealingly coupled to the chamberbody 330 using a flexible bellows 408. Alternatively or in combination,the motion assembly 410 may be configured to rotate the substratesupport 316.

Returning to FIG. 3, alternatively or in combination, one or moreradiative sources, such as lamps 323, may be provided to heat thesubstrate 314. The lamps 323 may be configured similar to radiativelamps utilized in rapid thermal processing chambers. Other heatingmethods or designs, including heating the substrate from above, may alsobe used.

The temperature of the substrate 314 may be controlled by stabilizing atemperature of the substrate support 316. A heat transfer gas from a gassource 348 is provided via a gas conduit 349 to channels formed by theback of the substrate 314 and grooves (not shown) in the support surfaceand/or chucking device 317. The heat transfer gas is used to facilitateheat transfer between the substrate support 316 and the substrate 314.During the processing, the substrate support 316 may be heated by theone or more resistive heaters 321 to a steady state temperature and thenthe heat transfer gas facilitates uniform heating of the substrate 314.Using such thermal control, the substrate 314 may be maintained at atemperature of about 0 to about 550 degrees Celsius.

In some embodiments, the substrate support 316 may have a low thermalmass for example, to prevent thermal shock to the substrate die to rapidcooling. For example, the substrate support 316 may be configuredwithout a heat sink or cooling plate coupled thereto, thereby limitingthe rate at which heat may be removed from the substrate support 316.

During a typical operation, the substrate 314 (e.g., the substrate 202)may be placed on the substrate support 316 and process gases aresupplied from a gas panel 338 through an entry port 326 disposed in theceiling 320 and centered above the substrate 314. In some embodiments,the gas panel 338 is configured to supply process gases such as ammonia(NH₃) or hydrogen (H₂). The process gases may be combined withadditional gases, for example, nitrogen (N₂), helium (He) or argon (Ar)and flowed into the chamber 310 via the entry port 326. The entry port326 may include, for example, a baffle or similar gas inlet apparatusthat can provide a process gas perpendicularly towards the substrate 314and radially onward into the process chamber 310. Upon entering theprocess chamber 310 via the entry port 326, the process gases form agaseous mixture 350. The gaseous mixture 350 is ignited into a plasma355 in the chamber 310 by applying power from the RF source 318 to theantenna 312. Optionally, power from the bias source 322 may be alsoprovided to the substrate support 316. The pressure within the interiorof the chamber 310 is controlled using a throttle valve 362 and a vacuumpump 336. The temperature of the chamber wall 330 is controlled usingliquid-containing conduits (not shown) that run through the wall 330.

The controller 340 comprises a central processing unit (CPU) 344, amemory 342, and support circuits 346 for the CPU 344 and facilitatescontrol of the components of the nitridation process chamber 310 and, assuch, of nitridation processes, such as discussed herein. The controller340 may be one of any form of general-purpose computer processor thatcan be used in an industrial setting for controlling various chambersand sub-processors. The memory, or computer-readable medium, 342 of theCPU 344 may be one or more of readily available memory such as randomaccess memory (RAM), read only memory (ROM), floppy disk, hard disk, orany other form of digital storage, local or remote. The support circuits346 are coupled to the CPU 344 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like. Theinventive method may be stored in the memory 342 as software routine andmay be executed or invoked in the manner described above. The softwareroutine may also be stored and/or executed by a second CPU (not shown)that is remotely located from the hardware being controlled by the CPU344.

Thus, methods and apparatus for forming nitrogen-containing layers havebeen provided herein. The inventive methods and apparatus mayadvantageously provide improved nitridation of a target layer (e.g., afirst layer) by facilitating increased nitrogen content with reducedlayer thickening, and improved oxygen retention at an interface betweenthe target layer and another device layer, for example, a polysilicongate.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

The invention claimed is:
 1. A method of forming a nitrogen-containinglayer, comprising: placing a substrate having a first layer disposedthereon on a substrate support of a process chamber, wherein the firstlayer is a 3-dimensional structure; heating the substrate to a firsttemperature of about 250 degrees Celsius to about 500 degrees Celsius;and exposing the first layer to an RF plasma formed from a process gascomprising ammonia (NH₃) to transform the first layer into thenitrogen-containing layer, wherein the process gas comprises about 0.5%to about 99.5% ammonia (NH₃) based on total gas flow and the balance isa noble gas, and wherein the plasma has an ion energy of less than about8 eV, and wherein an amount of nitrogen incorporated in a top surface ofthe nitrogen-containing layer is substantially equal to an amount ofnitrogen incorporated down a sidewall of the nitrogen-containing layer.2. The method of claim 1, wherein the RF plasma has an ion energy ofless than about 4 eV.
 3. The method of claim 1, wherein the noble gas isargon.
 4. The method of claim 1, wherein the ammonia (NH₃) is flowed atabout 15 sccm to about 500 sccm.
 5. The method of claim 1, furthercomprising exposing the first layer to the RF plasma while maintainingthe process chamber at a pressure of about 5 mTorr to about 500 mTorr.6. The method of claim 1, further comprising forming the RF plasma usinga pulsed RF power source having a frequency of about 13.56 MHz.
 7. Themethod of claim 6, wherein the pulsed RF power source supplies power atup to 2000 watts and at a duty cycle of up to 30%.
 8. The method ofclaim 6, wherein the pulsed RF power source supplies power at a dutycycle of about 5% to about 10%.
 9. The method of claim 1, wherein thefirst layer comprises a semiconductor material, a metal, or a metaloxide.
 10. The method of claim 9, wherein the first layer is silicon(Si), germanium (Ge), silicon germanium (SiGe), or a III-V compound. 11.The method of claim 9, wherein the first layer is tungsten (W), titanium(Ti), titanium nitride (TiN), tantalum (Ta),or tantalum nitride (TaN).12. The method of claim 9, wherein the first layer is titanium dioxide(TiO₂), or aluminum oxide (Al₂O₃).